Generally, when a vent port for discharging gas from a sealed space between a pair of plate glasses separated in a thickness direction is formed in either one of the pair of plate glasses, an exhaust hole is formed through the plate glass and a vent pipe is then vertically inserted into the exhaust hole.
Further, a sealant is interposed and heated to melt in a joining portion between a lower end of the vent pipe and an upper circumference of the exhaust hole on the plate glass, so that the sealant flows and is solidified to form a sealing member, thereby completing a vent port in the glass panel.
Then, decompression is performed by discharging gas from a space between the plate glasses through the vent port, followed by heating the glass pipe to close and seal a leading end of the glass pipe. Thus, the vent pipe inevitably protrudes from the surface of the glass panel.
FIGS. 1a to 1c are cross-sectional views of a conventional method for forming a vent port.
Referring to FIG. 1a, an exhaust hole 5, 6 is formed at one side of an upper plate glass 18.
Referring to FIG. 1b, a vent pipe 7 is inserted into an upper portion 6 of the exhaust hole and a sealant 8 is placed in a joining portion between the vent pipe 7 and the upper plate glass 18.
Referring to FIG. 1c, the sealant 8 is heated to melt and flow, and is then solidified to form a sealing member 19, thereby forming a vent port in the plate glass.
Then, gas is discharged from a space between the plate glasses through the vent port, and an upper portion of the vent port 7 is sealed.
FIGS. 2a and 2b are cross-sectional views of a conventional method of closing a vent port.
Referring to FIG. 2a, the top of the vent port 7 having the seal member 19 is covered with a cover 61 having an inlet for decompression.
Then, an upper portion of the vent pipe 7 is heated using a heater 62 while discharging gas from the space between the plate glasses 14, 18 through the inlet provided at one side of the cover 61.
Here, a sealant 15 is interposed between the plate glasses 14, 18 to block gas introduced from the outside while maintaining an interior space.
Referring to FIG. 2b, the upper portion of the vent pipe 7 is melted and closed.
The conventional method for forming and sealing the vent port on the plate glass has a problem of limiting processability when the plate glasses are subjected to post-processing, such as joining, multilayer processing, and the like, since a glass pipe used as a vent pipe protrudes from the surface of one of the sheets of plate glass.
Particularly, when the vent pipe is broken during a process of stacking or post-processing the plate glasses, vacuum or decompression in the space between the plate glasses is damaged. In order to prevent this problem, a protective cap may be further provided to the sealed upper portion of the vent port.
FIG. 3 is a cross-sectional view of a conventional protective cap for a vent port.
In FIG. 3, a protective cap 70 is provided to a protruding vent port including a sealing member 19 and a sealed glass pipe 7. In this case, the vent port can be protected from damage in post-processing, but there are limits in joining and multilayer processing.
In addition, for a conventional method for sealing the vent pipe, the glass pipe is heated to melting point. At this time, since the glass pipe must be heated above a softening point of general plate glass, the plate glass for the glass panel can disadvantageously be deformed.
FIG. 4 is a cross-sectional view of a glass panel which undergoes deformation during a process of sealing a vent port.
Referring to FIG. 4, a protruding vent port is formed on a glass panel including a sealant 15 and spacers 16 between two plate glasses 14, 18. At this time, a sealing member 19 is formed to seal an interface between the vent pipe 7 of the protruding vent port and the upper plate glass 18, and the sealant is heated and melts at a temperature above the softening point of the plate glass, causing damage of the upper plate glass 18.
To solve such problems, a vent port for decompressing a space between plate glasses when manufacturing a glass panel must be formed as low as possible, and studies have been conducted to develop a technique for efficiently sealing the vent port without damaging the glass panel. However, attractive results have not been achieved in the art.